The other temptation, especially when writing about a character whose the same gender as you, is to make them you. Oh, she loves the colour purple. She has curly hair. She drinks black coffee and loves books and the smell of cut grass and hates lavender and bad grammar... Oh, whoops. No, let me rethink... She hates coffee. Drinks water all the time. Likes to exercise. Her hair is straight, her eyes are dark. She likes cleaning toilets and being really cold all the time! Whoops. Suddenly you've made your own anti-self. Some strange, polar opposite of yourself who's as contrived as the one who was exactly like you.
With Thea, my lead, I've tried to give her a little bit of myself. It would be impossible not to put something of yourself into a character after all. But writing yourself is boring to read and obnoxious to write. Instead, I find things we have in common. She hates the smell of coffee, but she loves the way a book feels in her hand. She's calmer than me, but still a little nervous. I worry about the perfection thing. I want her to be kind and honest and cleaver. She has to be cleaver, because of where she comes from. And kindness suits her. But maybe she should lie a little? Maybe she should jump to the wrong conclusion sometimes, be more stubborn, less forgiving.
She needs some work yet, I think.